1. Field of the Invention
The present invention relates to a part mounter and a method for mounting parts, and more particularly, to a part mounter and a method for mounting parts by which the required time and the distance equipment must move for mounting parts is minimized and the position of the parts is precisely recognized.
2. Description of the Related Art
In general, electronic parts such as semiconductor packages are mounted on a printed circuit board by using a part mounter. The part mounter picks up electronic parts supplied by a part supply portion such as a tray feeder or a tape feeder using vacuum suction and mounts the electronic parts at predetermined positions on the printed circuit board. Here, a head unit moves the electronic part to an image sensor to obtain information on the posture of the part held by a suction nozzle. As the image sensor, a vision camera (a line CCD or an area CCD) is used. The image sensor detects state of the part held by the part suction portion so that information on the posture of the part is obtained. The part suction portion corrects the posture of the held part according to the image information and then mounts the part on the printed circuit board.
FIG. 1 is a perspective view showing the structure of a typical part mounter. Referring to the drawing, the part mounter includes a first Y-axis 12 and a second Y-axis 13, an X-axis 11 moving along the first and second Y-axes 12 and 13, and a head unit 14 installed to be capable of moving along the X-axis 11. A suction nozzle 15 is installed at the head unit 14 to be capable of rotating and moving up and down. A printed circuit board (PCB) 25 is transferred by a conveyer 19 to the position of a part to be mounted. The head unit 14 moves between part feeders 18a, 18b, 18c, 18d and 18e, and the PCB 25. The suction nozzle 15 moves up and down and/or rotates to hold a part and mounts it on the PCB 25. At least one among the part feeders 18a, 18b, 18c, 18d and 18e may be a tape feeder or a tray. During a mounting process, the head unit 14 passes above an image sensor 16. The image sensor 16 is fixed at one side of the part mounter and detects the part held by the suction nozzle 15 so that it corrects a positional error generated when a part is held by the suction nozzle 15. The image sensor 16, for example, may have an image detecting device such as a vision camera (a line CCD or an area CCD).
FIG. 2 is a view schematically showing the path along which the head unit 14 shown in FIG. 1 moves. Referring to the drawing, the suction nozzle 15 of the head unit 14 picks up a part from the part feeders 18a, 18b, 18c, 18d and 18e and then moves to the position directly above the image sensor 16. The image sensor 16 senses the part held by the suction nozzle 15. Through a detecting process performed by the image sensor 16, an error generated when the part is held by the suction nozzle 15 can be recognized. Next, the head unit moves above a mounting position P on the PCB 25. The suction nozzle 15 of the head unit 14 descends and mounts the part at the mounting position P of the PCB 25. Here, to correct an error recognized through the sensing process, the head unit 14 changes its position in the coordinate system or the suction nozzle 15 rotates and then the part is mounted.
In the part mounter having the above structure, since the head unit 14 must travel from the part feeders 18a, 18b, 18c, 18d and 18e to the part mounting position P on the PCB 25 through the image sensor 16, the path of movement is long and complicated. That is, since the image sensor 16 is fixed at a particular position, the head unit 14 must move to the position directly above the image sensor 16 so as to sense the state of the held part.
FIG. 3 is a view showing an image of a state in which a part is held by the suction nozzle 15, which is taken by an image sensing apparatus. Referring to the drawing, the center of the suction nozzle 15 matches the central point A of an image 121. That is, when the suction nozzle 15 picks up a part 111 and moves just above the image sensor 16, the center of the suction nozzle 15 is designed to match the center of the image sensor 16. Thus, when a sensing process is performed by the image sensor 16, the center point A of the image 121 substantially matches the center of the suction nozzle 15. This is because a typical image recognition apparatus is fixed at one side of a part supply portion of a part mounter and the head unit 14 moves to a particular position after moving along a set path, that is, the center of the suction nozzle 15 matches the center of the image 121.
When the image sensing is performed after the suction nozzle 15 has picked up a part, the positional information of the central point O of a part is recognized with information on the size and shape of the part. Next, information on the tilt of the part is recognized by the information on the shape of the part. As shown in FIG. 3, recognizing the distance separated in the X direction and Y direction between the central point A of the image 121 and the central point O of the part 111, and a rotational degree xcex8 is recognized and the separated distance and the rotational degree are compensated for.
However, to correct the error generated when the part is held, the image sensor 16 must be maintained in a fixed state. This is because the central point of the suction nozzle 14 must match the central point A of the monitor 121 to recognize the error when suctioning the part. Thus, if the central point of the suction nozzle 14 does not match the central point of the image 121 during the sensing process, performing correction an error is not possible. The positional information with respect to the nozzle is indirectly obtained and it is assumed that the above preconditions are met. Also, at least one of the image sensor 16 and the head unit 14 must be fixed.
To solve the above problems, it is an object of the present invention to provide a part mounter and a method for mounting parts so that part mounting work is performed quickly while correcting an error generated.
Accordingly, to achieve the above objects, there is provided a part mounter comprising a plurality of part feeders for storing and supplying a plurality of parts, a conveyer for transferring a printed circuit board, a head unit capable of moving and having a suction nozzle for picking up a part from the part feeders and mounting the part on the printed circuit board on the conveyer, and an image sensor installed to move along a path crossing a movement path of the head unit, for detecting an image of the part held by the suction nozzle.
It is preferred in the present invention that at least one reference portion, which is detected if not covered by the part when the image sensor detects an image of the part held by the suction nozzle, is provided at the head unit.
Also, it is preferred in the present invention that the image sensor moves close to the part feeder where a part is picked up.
Also, it is preferred in the present invention that the image sensor moves to a position where a path along which the head unit moves, between a position where a part is picked up from the part feeder and a position where the part is mounted on the printed circuit board, and a path along which the image sensor moves cross.
Also, it is preferred in the present invention that the image sensor is moved by a motor for providing a driving force, a ball screw rotated by the motor, and a bushing and a linear guide member installed at one side of the image sensor and coupled to the ball screw.
Also, it is preferred in the present invention that the image sensor is capable of moving by a linear motor.
Also, it is preferred in the present invention that the head unit is installed to be capable of moving along an X-axis which is installed to be capable of moving along a first Y-axis and a second Y-axis installed parallel to each other.
Also, it is preferred in the present invention that a pair of X-axes are installed to be capable of moving along a first Y-axis and a second Y-axis installed parallel to each other, and two head units are provided so that one can move along each of the X-axes, and two image sensors are provided close to both sides of the conveyer.
To achieve the above objects, there is provided a method for mounting parts which is achieved by recognizing a particular part feeder where a part to be mounted is contained among a plurality of part feeders, moving a head unit to a position for picking up a part on the part feeder, moving an image sensor installed to be capable of moving to a position close to the particular part feeder, picking up a part from the particular part feeder with a suction nozzle installed at the head unit, moving the head unit to a position above the image sensor, detecting an image of the part held by the suction nozzle, moving the suction nozzle to a printed circuit board from the image sensor, and aligning the part with the printed circuit board while determining and compensating for an error generated when the part is picked up, and mounting the aligned part on the printed circuit board.
It is preferred in the present invention that the method for mounting parts further comprises a step of recognizing whether the image sensor has moved to a position close to the particular part feeder after the image sensor was supposed to have moved to the position close to the particular part feeder.
Also, it is preferred in the present invention that the determining and compensating is performed by determining the coordinates of the center of the suction nozzle by detecting a position of a reference portion which is not covered by the part when the image is obtained, determining the coordinates of the center of the part from an image obtained by the image sensor, calculating a value of correction of the part position by determining an offset of the part from the displacement of the center of the part held by the suction nozzle from the center of the suction nozzle, and controlling a position for mounting the part with the suction nozzle according to the value of correction.
According to another aspect of the present invention, there is provided a method for mounting a part which is achieved by calculating an optimal movement path between a position for picking up a part from a part feeder and a position for mounting the part on a printed circuit board, moving a head unit to the position for picking up a part from a part feeder, calculating a position where a movement path of an image sensor crosses a path formed between the part feeder and the position for mounting the part along which the head unit moves, moving the image sensor to the crossing position, picking up a part with a suction nozzle of the head unit, moving the head unit to a position above the image sensor, detecting the part held by the suction nozzle by the image sensor, moving the head unit to the position for mounting the part on the printed circuit board, and aligning the part while determining and compensating for an error generated when the part is picked up, and mounting the aligned part.
It is preferred in the present invention that the method further comprises a step of recognizing whether the image sensor has moved to the cross position after the image sensor is moved to the cross position.